As of 2007, an estimated 1.3 million new cases of invasive breast cancer were expected to occur among women and an estimated 465,000 breast cancer deaths in women were expected to occur. Breast cancer is the most frequently diagnosed cancer in women and it is the leading cause of cancer death among women worldwide. (ACS 2007 Stats).
Up to 25% of women who present with early breast cancer have developed tumors which overexpress human epidermal growth factor receptor 2 (Her2/neu), usually as a result of erbB2 gene amplification. (Owens M A at al. Clin. Breast Cancer 5 (2004)). These tumors are considered to be Her2+ and are characterized by aggressive growth and division, which can result in high recurrence rates after initial treatment and poor prognosis. (Slamon D J, Clark G M, Wong S G, Levin W J, Ullrich A, McGuire W L. Human breast cancer: correlation of relapse and survival with amplification of the Her2/neuoncogene. Science, 1987; 235: 177-182).
One method to test for Her2+ tumors is to use immunohistochemistry (IHC) to measure the levels of receptor on cancer cell surfaces. The test is scored on a scale of 0 to 3+, where a score of 0=negative, 1+=negative, 2+=borderline, or 3+=positive based on a reviewer's interpretation of staining intensity and completeness of membrane staining.
Additionally, Her2 gene amplification is detected using a fluorescent in situ hybridization (FISH) test that quantifies the number of gene copies in the cancer cell nucleus. A number of reports have verified its accuracy both in freshly frozen and paraffin-embedded tumor material (Mitchell, M. S., Semin. Oncol, 26:108 (1999))). FISH is generally performed using either single-color (HER-2/neu probe only) or dual-color hybridization (using HER-2/neu and control probes (e.g., chromosome 17 centromere probes simultaneously), with the latter method making it easier to distinguish true HER-2/neu amplification from chromosomal aneuploidy. FISH using entire cells (e.g., cultured cells, pulverized tissue, or imprint touch specimens from tumors) is considered straightforward, but the use of tissue sections complicates the quantitative nature of FISH due to nuclear truncation (i.e., due to the slicing of the tissues during their preparation for staining).
Chromogenic in situ hybridization (CISH) operates according to the same principles as FISH, except polynucleotide probes are labeled with a chromogen rather than a fluorophore. CISH does not require a costly fluorescent microscope and CISH signals do not decay over time.
Trastuzumab (Herceptin®) was developed as a targeted therapy to combat Her2 overexpression. Trastuzumab is a humanized monoclonal antibody directed against the extracellular domain of Her2 and is therefore specific for its target. Trastuzumab is approved for the adjuvant treatment of Her2-overexpressing node-positive or node-negative breast cancer. Trastuzumab in combination with paclitaxel is approved for the first-line treatment of Her2-overexpressing metastatic breast cancer. Trastuzumab as a single agent is approved for treatment of Her2-overexpressing breast cancer in patients who have received one or more chemotherapy regimens for metastatic disease. Trastuzumab has been shown to be effective across all of its approved uses (C. Jakisch, Her2-positive metastatic breast cancer: optimizing trastuzumab-based therapy, Oncologist 11 (2006) 34-41; Gonzalez-Angulo, G. N. Hortobagyi, F. J. Esteva, Adjuvant therapy with trastuzumab for Her2/neu-positive breast cancer, Oncologist 11 (2006) 857-867; C. A. Hudis, Trastuzumab-mechanism of action and use in clinical practice. N. Engl. J. Med. 357 (1) (Jul. 5, 2007) 39-51.).
Unfortunately, not all patients with Her2+ tumors are responsive to trastuzumab treatment. Trastuzumab monotherapies only lead to tumor regression in approximately 30% of patients. Complicating the issue further is the fact that administration of trastuzumab with anthracyclines and cyclophosphamide, while effective, leads to cardiac events in 28% of the patients. (T. M. Suter. N. Cook-Bruns, C. Barton, Cardiotoxicity associated with trastuzumab (Herceptin) therapy in the treatment of metastatic breast cancer, Breast 13 (3) (June 2004) 173-183). Additionally, a trastuzumab-containing treatment regimen is expensive, costing up to $100,000 per year. Thus, in an effort to reduce dangerous side effects and provide the most effective treatment, it is imperative to further refine the process by which trastuzumab is prescribed to try to better identify who will be sensitive to treatment.
Currently, because of the cost and risk associated with trastuzumab treatment, only subjects that have Her2+ tumors are administered the drug. Amongst these trastuzumab-treated Her2+ patients, up to 30-50% of patients will not positively respond to the treatment. Furthermore, it is currently thought that patients with Her2− tumors will not benefit from trastuzumab treatment. Nonetheless, despite the response rate in Her2+ patients, and the unknown effects of treatment in Her2− patients, trastuzumab treatment decisions are currently based on the detection of elevated Her2 levels. The discovery of additional markers could improve treatment decisions and identify Her2− subjects who could benefit from receiving trastuzumab, while also refining the number of Her2+ subjects to those who could best benefit from treatment.